Subject or object questions?

Most of the questions we know are called 'object' questions because the information they are asking about would be the object of the affirmative sentece.

Where do you live?

What are you doing?

These questions use the general structure we use for interrogative sentences ( [Wh-]+Aux+S+V+[O]?).

When we want to know the subject of an action, the structure changes a bit:

How many people came to the party?

Who went to London on holidays?

In this case, the structure is similar to the one in an affirmative sentence (S+V+O), and the Wh- word works as the subject.

Look at the difference in meaning:

Who visited you last weekend? (Somebody visited you)

Who did you visit las weekend? (You visited somebody)

Exercise 1
Exercise 2